Recently, energy harvesting that derives power from energy in the environment (e.g. luminous energy, energy of ambient electromagnetic waves, mechanical vibrational energy and thermal energy) has become a hot research topic.
In order to utilize electric power derived from the energy harvesting as the power supply, for example, a DC-DC converter could be used to boost the voltage (for example, an ultra-low voltage of from several tens to several hundreds of mV) obtained from an ultra-low voltage generation unit (such as a photovoltaic electricity generator, an electromagnetic wave electricity generator, a vibration electricity generator, or a thermoelectric generator).
As described above, for utilization of electric power obtained from energy harvesting, the DC-DC converter (boost converter) could be used to boost an ultra-low voltage generated by the ultra-low voltage generation unit, and a voltage to drive the control circuit of boost converter is also obtained by the ultra-low voltage generation unit.
Specifically, a driving voltage for control circuit of the boost converter could be supplied by an auxiliary step-up unit that can boost the ultra-low voltage generated from the ultra-low voltage generation unit. The step-up unit further includes an oscillator and rectifiers.
In order to operate from ultra-low voltage, to ensure safety and to achieve high efficiencies, it is required that an oscillator in the auxiliary step-up unit be capable of oscillating from ultra-low voltage, regulating its output voltage amplitude and maintaining high efficiencies. However, the existing oscillators could not completely satisfy these requirements.
Conventionally, there have been various types of DC-DC converters applicable to energy harvesting.
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Patent Document 2: Japanese Examined Patent Application Publication No. H03-047067
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